JP6137468B2 - Semiconductor light emitting device - Google Patents

Description

  The present invention relates to a semiconductor light emitting device using a gallium nitride compound semiconductor.

Semiconductor light-emitting elements such as blue light-emitting diodes using gallium nitride-based compound semiconductors such as GaN (gallium nitride), GaAlN (gallium aluminum nitride), InGaN (indium gallium nitride), InGaAlN (indium gallium nitride aluminum) are known. .
A conventional typical light emitting device is an insulating substrate made of sapphire, and is disclosed in, for example, Japanese Laid-Open Patent Publication No. 4-297003 formed on one main surface (upper surface) of this insulating substrate. Where x is a numerical value in the range of 0 <x ≦ 1), an n-type semiconductor region made of a gallium nitride compound semiconductor (for example, GaN) formed by epitaxial growth on the buffer layer, An active layer made of a gallium nitride-based compound semiconductor (for example, InGaN) is formed on the n-type semiconductor region by the epitaxial growth method, and a p-type semiconductor region is formed on the active layer by the epitaxial growth method. The cathode electrode is connected to the n-type semiconductor region, and the anode electrode is connected to the p-type semiconductor region.

By the way, when sapphire is used as an insulating substrate, since sapphire is expensive, the cost of the light emitting element is increased. In order to solve such a problem, the cost is reduced by forming a nitride semiconductor layer on an inexpensive silicon substrate.
However, the lattice constant of the silicon substrate and the lattice constant of the nitride semiconductor layer are greatly different, and the thermal expansion coefficient is also different. For this reason, large strain energy is generated in the nitride semiconductor layer formed on the silicon substrate by epitaxial growth. As a result, the nitride semiconductor layer is likely to crack, and the crystal quality is likely to deteriorate.
In order to avoid this problem, for example, Japanese Unexamined Patent Application Publication No. 2003-115606 proposes a semiconductor light emitting device in which a nitride semiconductor buffer layer is disposed between a silicon substrate and a functional layer made of a nitride semiconductor. Has been.

Japanese Patent Laid-Open No. 4-297023 Japanese Patent Laid-Open No. 2003-115606

  In recent years, with the widespread use of such semiconductor light-emitting elements for lighting applications, improvement of element characteristics and reliability by further improvement of crystal quality of the semiconductor light-emitting elements and improvement of electrical conductivity have been demanded. In view of such problems, it is an object of the present invention to provide a semiconductor light emitting device capable of improving the crystal quality of an epitaxially grown film as compared with the prior art and capable of improving electrical conductivity.

According to one aspect of the present invention, a semiconductor light emitting device having a gallium nitride-based compound semiconductor, a substrate made of silicon or a silicon compound, a buffer layer disposed on one main surface of the substrate, and a light emitting function And a semiconductor region including a gallium nitride-based compound layer disposed on the buffer layer, wherein the buffer layer is AlxGa1-xN (where x is a numerical value satisfying 0 <x ≦ 1). A second layer consisting of GaN or AlyGa1-yN (where y is a numerical value satisfying y <x and 0 <y <1), and AlzGa1-zN. (Where z is a numerical value satisfying y <z ≦ x), and the second layer and the third layer are alternately laminated to form a composite layer. The buffer layer is formed by alternately stacking the first layer and the composite layer. The average Al composition of the entire layer is in the range of 14 to 30%, and the average Al composition of the entire semiconductor region is 3% or less .

  According to the present invention, it is possible to provide a semiconductor light-emitting element capable of improving the crystal quality of an epitaxially grown film as compared with the prior art and capable of improving electrical conductivity.

It is a schematic diagram which shows the structure of the semiconductor light-emitting device concerning embodiment of this invention. It is the table | surface which compared the characteristic of the conventional example and the semiconductor light-emitting device which concerns on embodiment of this invention. It is the figure which showed the crack length which arose in the epitaxial film of the semiconductor region with respect to the change of the average Al composition of the whole buffer layer of the semiconductor light-emitting device concerning embodiment of this invention. It is a schematic diagram which shows the structure of the modification of the semiconductor light-emitting device which concerns on embodiment of this invention.

  Next, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic and ratios of thicknesses of the respective regions are different from actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

A blue light emitting diode 1 according to the embodiment of the present invention shown in FIG. 1 includes a semiconductor region 10 composed of a plurality of gallium nitride compound layers for obtaining a light emitting function, and a silicon semiconductor whose principal plane crystal plane orientation is (111). And a substrate 11 and a buffer layer 12.

The semiconductor region 10 having a light emitting function includes an n-type semiconductor region 13 as a first semiconductor region made of GaN (gallium nitride), a light-emitting layer or active layer 14 made of p-type InGaN (indium gallium nitride), and a second layer. And a p-type semiconductor region 15 made of GaN (gallium nitride) as the semiconductor region. An anode electrode 17 as a first electrode is formed on one main surface (upper surface) of the base 16 formed of a laminate of the substrate 11, the buffer layer 12, and the semiconductor region 10 having a light emitting function, that is, on the surface of the p-type semiconductor region 15. A cathode electrode 18 as a second electrode is disposed on the other main surface (lower surface) of the base 16, that is, the other main surface of the substrate 11. The buffer layer 12, the n-type semiconductor region 13, the active layer 14, and the p-type semiconductor region 15 are epitaxially grown on the substrate 11 with the respective crystal orientations sequentially aligned.

The substrate 11 is made of a silicon single crystal containing a conductivity determining impurity. The impurity concentration of the substrate 11 is about 5 × 10 18 cm −3 to 5 × 10 19 cm −3, and the resistivity of the substrate 11 is about 0.0001 Ω · cm to 0.01 Ω · cm. The substrate 11 of this embodiment is made of n-type silicon into which As (arsenic) is introduced. The substrate 11 having a relatively low resistivity functions as a current path between the anode electrode 17 and the cathode electrode 18. The substrate 11 has a relatively thick thickness of about 350 μm, and functions as a support for the semiconductor region 10 having the light emitting function and the buffer layer 12 including the p-type semiconductor region 15, the active layer 14, and the n-type semiconductor region 13. To do.

The buffer layer 12 disposed on the substrate 11 has a multilayer structure in which a plurality of first layers 12a, a plurality of second layers 12b, and a plurality of third layers 12c are stacked in a certain order. In FIG. 1, the first layer 12a, the second layer 12b, the third layer 12c, the second layer 12b, the third layer 12c, the second layer 12b, and the first layer 12a are formed on the substrate 11. The layers are repeatedly formed in order. In other words, the composite layer 20 formed by repeatedly laminating the second layer 12b and the third layer 12c and the first layer 12a are alternately laminated to form the buffer layer 12 having a multilayer structure. The
In FIG. 1, for convenience of illustration, the buffer layer 12 is formed by repeating the composite layer 20 and the first layer 12 a twice. Actually, however, the buffer layer 12 is composed of the composite layer 20 and the first layer. 12a is repeated 60 times.

The first layer 12a includes Si (silicon) as an n-type conductivity determining impurity and has a chemical formula of Al _x Ga _1-x N, where x is an arbitrary value satisfying 0 <x ≦ 1 It is made of a material that can That is, the first layer 12a is made of AlN (aluminum nitride) or AlGaN (aluminum gallium nitride). In the embodiment of FIG. 1, AlN (aluminum nitride) corresponding to a material in which x in the above formula is 1 is used for the first layer 12a. Although AlN of the first layer 12a has an insulating property, in the embodiment, Si (silicon) as an n-type conductivity determining impurity is included, so that the electric resistance is relatively small.

The second layer 12b is made of GaN (gallium nitride) or a chemical formula Al _y Ga _1-y N, where y is a material that can be expressed by any numerical value satisfying y <x and 0 <y <1. It is a very thin film of n-type semiconductor. When an n-type semiconductor composed of Al _y Ga _1-y N is used as the second layer 12b, y is set to 0 <y <0.3 in order to suppress an increase in the electric resistance of the second layer 12b. It is desirable to satisfy a satisfactory value, that is, greater than 0 and less than 0.3. This is because when y is 0.3 or more, the efficiency of impurity doping decreases, the carrier density decreases, and the electrical resistance increases. In this embodiment, the second layer 12b is made of GaN so as to reduce the electric resistance. The second layer 12b desirably includes silicon as an n-type impurity.

The third layer 12c has the formula Al _z Ga _1-z N, where, z is an arbitrary numerical value, n-type semiconductor of very thin film made of a material which can be shown by satisfying the y <z ≦ x is there. When an n-type semiconductor composed of Al _z Ga _1-z N is used as the third layer 12c, the electrical conductivity of the composite layer 20 in which the second layer and the third layer are alternately stacked is set. In order to improve, it is desirable that z is a value satisfying y <z and 0 <z <0.5, that is, larger than y and smaller than 0.5. At the heterointerface formed between the third layer 12c and the second layer 12b, a carrier pool formed by band discontinuity occurs. By setting z to y <z and 0 <z <0.5, the electric conduction in the direction along the interface, that is, the in-plane direction of the blue light emitting diode 1 is dramatically improved.
Preferably, zy> 0.1, more preferably zy> 0.2. Thereby, the light emission uniformity in the in-plane direction of the blue light emitting diode 1 is dramatically improved.
On the other hand, when z is 0.5 or more, the impurity doping efficiency is reduced and the carrier density is lowered, and the vertical electric resistance of the third layer 12c, that is, the electric current from the substrate 11 toward the semiconductor region 10 is obtained. Resistance will increase.
In this embodiment, the second layer 13b is made of Al _0.2 Ga _0.8 N so as to increase the electric conduction in the in-plane direction and minimize the electric resistance in the vertical direction. The third layer 12c desirably includes silicon as an n-type impurity.

The thickness of the first layer 12a of the buffer layer 12 is preferably 0.5 nm to 10 nm, more preferably 1 nm to 8 nm. When the thickness of the first layer 12a is less than 0.5 nm, the flatness of the semiconductor region 10 formed on the upper surface of the buffer layer 12 cannot be kept good. When the thickness of the first layer 12a exceeds 10 nm, the quantum mechanical tunnel effect cannot be obtained satisfactorily, and the electrical resistance of the buffer layer 12 increases.

The thickness of the second layer 12b is preferably 2 nm or more and less than 10 nm, and more preferably 6 nm or more and less than 10 nm. When the thickness of the second layer 12b is less than 2 nm, the flatness of the buffer layer 12 and further the flatness of the semiconductor region 10 formed thereon cannot be maintained well. If the thickness is 10 nm or more, cracks occur in the epitaxial film.

The thickness of the third layer 12c is preferably 0.5 nm to 2 nm, more preferably 0.75 nm to 1.5 nm. When the thickness is less than 0.5 nm, the effect of improving electrical conduction in the direction along the interface, that is, the in-plane direction of the blue light emitting diode 1 cannot be obtained. On the other hand, when the thickness is 2 nm or more, the electrical resistance in the vertical direction, that is, the electrical resistance from the substrate 11 toward the semiconductor region 10 increases.

There is a composite layer 20 in which the second layer 12b and the third layer 12c are alternately stacked, and the average Al of the entire buffer layer 12 in which the first layer 12a and the composite layer 20 are at least alternately stacked. The composition is 14 to 30%, and the average Al composition of the entire semiconductor region 10 including a plurality of gallium nitride compound layers disposed on the buffer layer 12 is set to 3% or less. As a result, the internal strain balance between the buffer layer 12 and the semiconductor region 10 becomes appropriate, cracks generated in the epitaxial film can be suppressed, and the crystal quality of the semiconductor region 10 can be improved.
When the semiconductor region 10 is a light emitting diode, a transistor, a light receiving element, or a power generating element, by making the average Al composition of the entire semiconductor region 10 3% or less, cracks can be suppressed and a semiconductor element with few crystal defects can be obtained. it can.

Further, in order to improve the crystal quality of the semiconductor region 10, it is necessary to increase the epitaxial film thickness of the semiconductor region 10. However, for example, as in the conventional example shown in Patent Document 2, the first layer 12a (AlN) is 0.5 to 10 nm thick, and the second layer 12b (GaN) is repeatedly 10 to 300 nm thick. In the formed buffer layer, there is a problem that cracks occur in the epitaxial film when the thickness of the semiconductor region 10 is increased. This is because the second layer 12b is as thick as 10 to 300 nm, so that stress relaxation is not sufficiently performed in the buffer layer.

FIG. 2 shows the semiconductor region 10 in the buffer layer 12 according to the present invention and the buffer layer (without the third layer 12c) by repeating the first layer 12a and the second layer 12b according to the conventional example. It is the figure which compared the crack length (mm) which arose in the epitaxial film. Specifically, in the buffer layer 12 according to the present invention, the first layer 12a is made of AlN with a thickness of 5 nm, the second layer 12b is made of GaN with a thickness of 8 nm, and the third layer 12c is made of Al _0.2 Ga _0.8 N. Formed. The comparison was performed with a structure in which the thickness of the third layer 12c was changed (Comparative Example 1: 0.75 nm, Comparative Example 2: 1 nm, Comparative Example 3: 1.25 nm).
Further, as the buffer layer according to the conventional example, the first layer 12a was formed with AlN at 5 nm, and the second layer 12b was formed with GaN at 24 nm without including the third layer 12c.

As shown in FIG. 2, the crack length generated in the epitaxial film in the structure of the conventional example is 10 mm, whereas in the structure of the buffer layer 12 according to the present invention, 3 mm in Comparative Examples 1 and 3 and 2 mm in Comparative Example 2 It is. Therefore, in the structure of the buffer layer 12 according to the present invention, the crack length generated in the epitaxial film of the semiconductor region 10 is shorter than in the conventional example, and the effect of disposing the third layer 12c is noticeable. I understand that That is, rather than forming the second layer 12b with a thickness of 24 nm as in the conventional example, the second layer 12b has three layers with a thickness of 8 nm as in the buffer layer according to the present invention, and between the second layers 12b. By adopting a structure in which the third layer 12c is arranged, the stress in the buffer layer 12 is sufficiently relaxed, and the occurrence of cracks in the epitaxial film in the semiconductor region 10 can be suppressed. At this time, the conditions under which the crack was most suppressed were that the average Al composition of the entire composite layer 20 was 10% or less, and the third layer 12c was Al _z Ga _1-z N (z <0.5). Is the case.

Furthermore, adjusting the average Al composition of the entire buffer layer 12 is also important for suppressing cracks. FIG. 3 shows the crack length generated in the epitaxial film of the semiconductor region 10 with respect to the change in the average Al composition of the entire buffer layer 12. As shown in FIG. 3, the crack length of the epitaxial film in the semiconductor region 10 is suppressed to less than 5 mm by setting the average Al composition of the entire buffer layer 12 to 14 to 30%. This is because when the average Al composition of the entire buffer layer 12 is less than 14 to 30%, compressive stress due to an average lattice constant difference between the semiconductor region 10 and the buffer layer 12 can be applied to the semiconductor region 10. It is. Thereby, the tensile stress resulting from the difference in thermal expansion coefficient between the semiconductor region 10 and the substrate 11 is relaxed, and the total internal stress of the semiconductor region 10 can be reduced.
However, when the average Al composition of the entire buffer layer 12 is less than 14%, effective compressive stress cannot be applied to the semiconductor region 10, and cracks and crystal defects are generated. In addition, if the average Al composition of the entire buffer layer 12 exceeds 30%, the tensile stress generated in the buffer layer 12 increases, and the buffer layer 12 itself causes cracks.
Therefore, the crack which arises in the epitaxial film of the semiconductor region 10 can be suppressed by setting the average Al composition of the entire buffer layer 12 to 14 to 30%.

Further, in order to apply an effective compressive stress to the semiconductor region 10, it is preferable that the first layer 12 a and the composite layer 20 be alternately stacked repeatedly 20 times or more. This is because compressive stress is applied to the semiconductor region 10 by increasing the film thickness of the entire buffer layer 12. More preferably, the number of repetitions is 50 times or more.

In the embodiment of FIG. 1, the thickness of the first layer 12a is 5 nm, the thickness of the second layer 12b is 8 nm, the thickness of the third layer 12c is 1 nm, and the entire buffer layer 12 is formed. Was formed to have a thickness of 1865 nm.

FIG. 4 shows a modification of the semiconductor light emitting device according to the embodiment of the present invention. Nitride containing In only on the side close to the substrate 11 of the buffer layer 12 in which the first layers 12a and the composite layer 20 are alternately stacked, that is, between the buffer layer 12 and one main surface of the substrate 11 By inserting the semiconductor layer 19, the contact resistance between the substrate 11 and the buffer layer 12 can be reduced. For example, by forming a layer of In _0.05 Ga _0.95 N on the substrate 11 with a thickness of 10 to 50 nm and forming the buffer layer 12 with the first layer 12a formed thereon, the contact resistance between the substrate 11 and the buffer layer 12 is reduced. Can be reduced.
Further, for example, after the first layer 12a is formed on the substrate 11, a layer of In _0.05 Ga _0.95 N is inserted by 10 to 50 nm, and the buffer layer 12 having the first layer 12a formed thereon is formed. The contact resistance between the substrate 11 and the buffer layer 12 can be reduced.
This is because the addition of In increases the difference in lattice constant and band gap at the interface with the first layer 12a, increasing the density of carriers generated locally at the heterointerface and reducing the contact resistance. It is.

As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

DESCRIPTION OF SYMBOLS 1 ... Blue light emitting diode 10 ... Semiconductor region 11 ... Substrate 12 ... Buffer layer 12a ... 1st layer 12b ... 2nd layer 12c ... 3rd layer 13 .. n-type semiconductor region 14... Active layer 15... P-type semiconductor region 16 .. base 17... Anode electrode 18. ..Composite layer

Claims (2)

A semiconductor light emitting device having a gallium nitride compound semiconductor,
A substrate made of silicon or a silicon compound;
A buffer layer disposed on one main surface of the substrate;
A semiconductor region including a gallium nitride-based compound layer disposed on the buffer layer to obtain a light emitting function;
The buffer layer comprises:
A first layer made of Al x Ga 1-x N (where x is a numerical value satisfying 0 <x ≦ 1);
A second layer made of GaN or AlyGa1-yN (where y is a numerical value satisfying y <x and 0 <y <1);
A third layer made of AlzGa1-zN (where z is a numerical value satisfying y <z ≦ x);
Have
The second layer and the third layer are alternately stacked to form a composite layer,
The first layer and the composite layer are alternately stacked ,
An average Al composition of the entire buffer layer is in a range of 14 to 30%, and an average Al composition of the entire semiconductor region is 3% or less . 2. The semiconductor light emitting element according to claim 1 , wherein an average Al composition of the entire composite layer is 10% or less, and the third layer is AlzGa1-zN (z <0.5).

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